The drug discovery landscape has been transformed by the genomics revolution. Advances in the understanding of biomolecular pathways and the roles they play in disease will lead to vast numbers of targets for therapeutic intervention. GPCRs represent the most important collection of therapeutic targets available.
GPCRs are proteins that tranduce signals across a cell membrane. They consist of a single polypeptide chain that threads back and forth seven times across the phospholipid bilayer that forms the cell membrane. The polypeptide chain has a portion inside the cell which form a G-protein coupling domain, and a receptor portion outside or in the cell wall. A signal molecule interacts with the receptor which sends the signal through the membrane wall and the signal causes the G-protein coupling domain to interact with a G protein.
Over 50% of marketed drugs target GPCRs. Whilst the druggable extent of GPCRs numbers some 450 receptors only some 200 GPCRS have been matched with their ligands. Orphan receptors suitable for drug targeting may therefore number in excess of 200 receptors. These are receptors with less than approximately 45% sequence identity to known GPCRs for which ligands have not been identified.
The targets of current GPCR drugs include, pain and inflammation, cancer, metabolic and gastrointestinal, cardiovascular and central nervous system disorders.
There is a continuing demand for new therapeutics, especially as our understanding of biological processes expands from the genomics revolution. The aforementioned GPCRs are suitable targets for therapeutic intervention due to their roles in such disorders as cancers, obesity and erectile dysfunction.
Considering the rate of generation and nature of the targets currently being deconvoluted by biologists, there is a need for the development of drug candidates, designed in a rational manner to purposely interact with selected targets, such as the GPCRs.
From a drug discovery perspective, carbohydrate pyranose and furanose rings and their derivatives are well suited as templates. Each sugar represents a three-dimensional scaffold to which a variety of substituents can be attached, usually via a scaffold hydroxyl group, although occasionally a scaffold carboxyl or amino group may be present for substitution. By varying the substituents, their relative position on the sugar scaffold, and the type of sugar to which the substituents are coupled, numerous highly diverse structures are obtainable.
An important feature to note with carbohydrates, is that molecular diversity is achieved not only in the type of substituents, but also in the three dimensional presentation. The different stereoisomers of carbohydrates that occur naturally, offer the inherent structural advantage of providing alternative presentation of substituents.
Employing a related methodology, Hirschmann et al (Hirschmann, R., et. al., J. Am. Chem. Soc., 1992, 114, 9217-9218, U.S. Pat. No. 5,552,534, WO 97/28172, WO 95/11686) synthesised several compounds designed as somatostatin analogues and integrin binders. The methodology employed by Hirschmann relied on protracted, linear, non-combinatorial syntheses, employed exclusively non-aminated pyranoses, and did not exploit any epimerisation chemistry to allow greater access to structural diversity. Consequently, these compounds and methods are manifestly distinct from this present invention.
We have developed a system that allows the chemical synthesis of highly structurally and functionally diverse derivatised carbohydrate and tetrahydropyran structures, of both natural and unnatural origin. The diversity accessible is particularly augmented by the juxtaposition of both structural and functional aspects of the molecules.
Using the axioms of this drug discovery methodology, we synthesised several novel classes of chemotypes in an effort to develop drug candidates against GPCR targets.